Mopar Performance Parts - Horsepower Hop-Up

At the very heart of the idea of hot rodding is the notion of taking something you've got and then pulling out the wrenches to make it better. The '71 Plymouth Satellite we recently acquired illustrates this sentiment precisely. Although camouflaged with enough grease to fool you, the engine actually ran pretty sweet. But even before the cash changed hands on the initial buy, thoughts were flying about how to make it better. Under the hood, we could look at the parts combination and spy some items we knew left plenty of room for improvement.

2/13In the boiler room of our newly acquired '71 Satellite sat a 340 engine of unknown history, though we could tell it ran pretty well, even under the GM air cleaner and through a set of factory 318 exhaust manifolds. We probably wouldn't have touched it hadn't the cam bolt worked loose, foiling the fuel pump drive. We could have put it back together from here but couldn't bring ourselves to do it without cleaning up the greasy muck.

The previous owner had installed a 340--a Mopar engine known for surprising power even in stock form--but in place of the rare and somewhat valuable 340 high-performance exhaust manifolds hung a lowly and restrictive set of 318 iron. Up top, under the misplaced GM air cleaner, the picture improved with an aftermarket single-plane Edelbrock intake manifold. However, this was no modern-day casting, just an obsolete Streetmaster, more commonly found decorating swap meet tables. A fairly fresh Edelbrock 600-cfm AFB was part of the package, but what was inside was anyone's guess. It was ripe for some speed parts upgrades, a decision finalized when we learned we'd have to tear into it to fix a loose cam bolt (which we discovered when the fuel pump wouldn't pump).

Diving InDigging into the 340 to get to that forsaken cam bolt meant we could just as easily stab in a new cam while we were at it. Though the engine was apart and ready to go back together, instead, looking at the caked grime, the decision was made to keep on going and pull the engine to clean and inspect it. What we found was a nice 0.040-inch-over 340 block with negligible bore wear filled with TRW/Speed-Pro L2316F-forged pistons. These are rated at a nominal 10.5:1 compression as a stock replacement for '68 to '71 340 engines with a positive deck of 0.018 inch (out of the hole) and deliver an actual compression ratio of more like 9.8:1 with typical factory small-block cylinder heads. The crank is a stock forged unit with the telltale signs of a performance balancing job. We also found good bearings, balanced stock rods, and a cam of unknown origin with a dead-smooth idle. Topping the short-block were later-model, small-valve (1.88/ 1.600-inch) No. 587 factory castings from a 360 engine.

There was no denying it was somewhat a bastard child, part racy, part stock, but in surprisingly nice condition. We just cleaned it up, repainted it, and put it all back together exactly like it was, with the exception of a stock 340hp-spec cam and lifters from Performance Automotive Warehouse's Superstock Industries line. Sure, we could have done a lot more, but we wanted to know what kind of power it made as we got it and more importantly, just how much power our changes would gain. This is where our pal Tom Habrzyk comes in. Habrzyk's shop, Advanced Performance Engineering in Palmdale, California, is equipped with a Dynojet chassis dyno, so we could quantify the value of our strictly bolt-on performance plan.

Phase 1: BaselineWe drove the Plymouth to Habrzyk's digs outside Palmdale and were surprised at how strong it felt. It wasn't wickedly fast by any stretch, mind you, but somewhat more stout than we would have expected from a small-block '71 B-Body equipped as it was. Habrzyk prepped the Satellite by installing a bung in the exhaust for a Lambda sensor to read air/fuel and strapped it to the rollers. With the timing set at 35 degrees total, it made 212 hp at a 4,800-rpm peak--not exactly sizzling, but not bad considering the 318 log exhaust manifolds, antique intake, stock cam, and regular stock 360 smog heads.

As an aside, we were running a stock dual-snorkel air cleaner as would be OEM equipment on a high-performance '71 Mopar. The oldest and cheapest trick in the book is to flip the lid on the air cleaner to expose the case to more airflow. Interestingly, it worked, adding 4 hp to the peak output, bringing it to 216 hp at 4,800 rpm. We carefully examined the air/fuel numbers from the Lambda and found the Edelbrock carb was dead-nuts-on at an average air/fuel ratio of 12.7:1.

3/13

The engine was pulled for inspection, cleaning, and detailing. It featured plain small-valve 360 heads, an Edelbrock Streetmaster intake, a 600-cfm Edelbrock carb, and a balance forged crank stock rotating assembly swinging old TRW +040 2316F forged pistons in fresh-looking bores. We stabbed in a PAW reproduction 340hp cam to replace the mild unknown cam the engine came with to give us a known baseline spec. The engine cleaned up well.

4/13

We brought the Satellite to Tom Habryzk's Advanced Performance Engineering aiming at adding power to the little 340 while quantifying the value of our bolt-on plans on his Dynojet chassis dyno. In baseline form as described above, we had 212 rear-wheel horsepower. For our first trick, we flipped the lid on the factory Mopar dual-snorkel air cleaner and found it worked. The engine gained 4 hp, and all further testing was done in this configuration, breathing through a Fram air filter.

Phase 2: Edelbrock Air-Gap IntakeThe first logical place to look for power is naturally where it would be easiest to get, and that's up top. The old Streetmaster intake was designed to be a compromise between mileage and power on moderate or near-stock engines back in the '70s and hence has small cross-section runners in a single-plane configuration and an unusual necked-down plenum of modest volume. In contrast, the Air-Gap is one of Edelbrock's latest and most successful designs, taking advantage of a two-plane, 180-degree runner layout that tunes for more torque and with high-flowing runners of ample cross section divorced from the lifter valley plate for a cooler, denser charge. On the engine dyno, it never fails to produce excellent results on moderate to strong street engines. The manifold swap was easily accomplished, leaving everything else the same, but with a regimen carried out throughout testing of monitoring air/fuel ratio and making changes as required.

The Air-Gap lived up to expectations here, raising the entire power curve right from the bottom of our test rpm range with a gain of 22 hp at 3,000 rpm and holding a similar gain right up to the top of our test at 5,500 rpm. Peak power with no other changes was now 231 at 5,000 rpm. The Air-Gap made the engine better everywhere, even on this relatively mild combination.

5/13

We suspected the outdated single-plane Streetmaster intake (right) would provide some room for improvement, so we replaced it with a dual-plane Edelbrock Performer RPM Air-Gap. Our familiarity with the Air-Gap in engine dyno testing shows it just works in street applications from mild up to 6,500 rpm. Although a single-plane normally favors top end output in comparison with a two-plane, the roles are reversed, considering the two specific intakes involved here. The Streetmaster was designed for low-end torque and economy on low-compression engines of the '70s with an unusual necked-down plenum and very small runner cross sections.

6/13

In comparison with the Streetmaster, the Air-Gap is considerably taller, though it fit beneath the standard hood in our Satellite with the OEM air cleaner. We reinstalled the 600 Edelbrock carb and tested to find power was up substantially everywhere, showing a solid gain across the engine's operating range. This was good.

Phase 3: TTI HeadersIf anything on our engine combination looked out of place in a performance application, it was those log-style 318 exhaust manifolds. We suspected a set of 4-into-1 headers would be a vast improvement, but for small-block Mopars, often the fit and ground clearance leave something to be desired. Tube Technologies Incorporated (TTI) is a company known to Mopar enthusiasts for making a product of exceptional quality and fit, so the next step was a set of TTIs featuring 1 5/8- to 1 3/4-inch stepped primaries and 3-inch collectors. For a column-shift car such as this Satellite, headers will interfere with the shift linkage cross-shaft, but TTI has a cleverly designed replacement that is a direct bolt-in. The existing 2 1/4-inch compression-bent H-pipe system was pruned back with a Sawzall to make way for the headers. The existing exhaust system featured Flowmaster mufflers and 2 1/4-inch tailpipes all the way back, and this was retained. Habrzyk fabricated a pair of reducers and used some of the surplus tubing we previously removed to connect the exhaust system. There was little doubt that the headers unlocked a worthy amount of power, with the gains apparent right from the start of our pull at 3,000 rpm and the gap widening with more power coming on as the tach climbed. We now had a respectable 251 hp, a gain of 20 hp at the peak, and a fatter power curve across the board. That's not bad considering the stock 340 cam and factory small-valve heads.

7/13

As we got it, the Satellite came with 318 exhaust manifolds feeding a compression-bent 2 1/4-inch H-pipe system dumping into Flowmaster mufflers with full 2 1/4-inch tailpipes. Those manifolds seemed like a place we could find power, especially when compared with full-tube headers from TTI.

8/13

As we've come to expect from TTI, the headers fit perfectly with plenty of ground clearance and no need to pull out the hammers. Habryzk fabricated reducers and hooked the headers' 3-inch collectors to the existing 2 1/4-inch system. Power was up everywhere, and we now had more than 250 hp to the wheels. This was too easy.

9/13Digging in for a cam change was the most involved part of our plan. We removed the 340-spec cam to make way for a Comp XE268H hydraulic flat-tappet. This Comp cam makes a nice compromise in power versus driveability for a regularly street-driven vehicle. We found 10 hp in the cam swap, even though it was working the valves in a set of substandard 360 smog heads.

Phase 4: Comp XE268H CamThe old 340 cam was a decent piece in its day and a big part of why those 340 Mopars of yesterday garnered an enviable reputation. The specs of the automatic trans cam (manual trans cars in 1968 came with a hotter stick) read 210/220 degrees duration at 0.050-inch lifter rise and 268/276-rated duration with 0.429/0.449-inch gross valve lift on a 114-degree lobe-separation angle. It would be fair to say these specs were healthy, considering the times and an OEM application.

Our replacement is from Comp Cams and like the stocker, it is a flat-tappet design, allowing us to retain the OEM valvetrain. The XE268H we selected is a mid-level offering from Comp's Xtreme Energy line of aggressive, fast-rate, flat-tappet hydraulic cams. The quick ramp profiles provide a good balance of torque and driveability for a given performance level when compared with older and slower-acting designs. Specs for this stick come in at 224/230 degrees duration at 0.050 inch and 0.477/0.480-inch lift on a 110-degree lobe-separation angle. Given that it's a good 14 degrees longer and nearly 0.050 inch taller than the stock cam on the intake and 4 degrees tighter on the lobe spread, it is definitely more cam, so we expected a little more chop at idle and a little less vacuum. While the idle will definitely let you know it's there, it is docile enough for daily street use.

As Habrzyk let it pull against the rollers, we showed parity with the OEM cam to about 3,500 rpm and a gain of 10 hp at the top of the pull. While that was a decent gain for the effort, we had performed exactly this same cam swap on the engine dyno before with a greater power spread showing. It just goes to show the importance of the complete combination. In our previous dyno work, we had big-valve heads that could really take advantage of the increase in cam. The old small-valve No. 587 castings on our 340 were never inspected, and upon later scrutiny we weren't surprised to see a horrible seat form with a factory counter bore straight down from the undersized 45-degree seat cut.

Phase 5: Mopar P5153849 Aluminum LA HeadsIt was pretty clear that getting more power from this 340 would require something be done with the heads. The No. 587 castings can be modified with larger valves, cut with a race-style seat form, and with extensive porting can flow very well. Now, throw new springs, retainers, seals, and guides into the mix, and maybe seats on the exhaust, and you've got some serious change wrapped up in that old iron. Instead, we turned to Mopar Performance for an out-of-the-box fix with new aluminum heads, PN P5153849.

These Mopar heads are a direct bolt-on replacement for stock and come fitted with a 2.02/1.60 valve combination and stout single springs (with damper) rated for up to 0.575-inch lift. The intake port layout is conventional and retains compatibility with the OEM-style valvetrain, while the intake port volume is 171 cc and the closed chamber measures 63 cc. The heads shave a good 50 pounds off the nose of the car, and we expected them to be quite an improvement over the old iron, especially in light of what we saw once the old heads were pulled and inspected. Since our engine is fitted with early 340-spec pistons, which are positive deck with the pistons 0.018 inch out, we used Fel-Pro No. 8553PT, 0.055-inch-thick gaskets for adequate piston-to-head clearance.

The cylinder heads were once again a bump to the top-end power with a gain of 30 hp pushing output to 291 hp at 5,200 rpm. Top-end power at that rpm had increased by a full 88 hp, while peak-to-peak output was improved by 79 hp compared with the baseline starting point.

10/13

Mopar's new P5153849 LA aluminum heads bear a striking similarity to the familiar Edelbrock Performer RPM heads and feature closed 63cc chambers and 2.02/1.60-inch valves. The heads drop approximately 50 pounds compared with the iron they replace and added 30 hp to the wheels.

11/13

We needed to take the pictures, so Habryzk did the heavy lifting, removing the hefty No. 587 iron heads. These showed a poor valve seat form and came with the standard 1.88/1.60-inch valve combination you'd find on a mid-'70s Mopar 360.

12/13With the 340 small-block pushing ever closer to 300 hp at the rear wheels, we reasoned it could benefit by upgrading from our baseline 600 Edelbrock AFB. The carb was swapped for an Edelbrock Thunder Series AVS in the 800-cfm capacity, giving us 302 hp at the rollers.

Phase 6: Edelbrock 800 Thunder Series AVS CarbWith the hefty increase in top end from our modifications, there was no denying that the engine was demanding more air at the higher end of the rev range. We still had the 600-cfm No. 1406 AFB-style Edelbrock carb from our baseline and had to question whether it was enough to keep up at the higher power levels. Our preference was to retain a similar style of carb for compatibility with the OEM dual-snorkel air cleaner assembly and retain the custom-bent fuel lines we had fabricated for the AFB carb, while providing for increased airflow. The Edelbrock Thunder Series AVS met these needs on every count, being a very similar derivative of the baseline carb's design. The main difference with the AVS is an adjustable spring-loaded air valve above the venturi in contrast to the nonadjustable counterweighted velocity valve found under the venturi with the AFB-style carb. We selected the 800-cfm carburetor, No. 1812, to ensure plenty of capacity. We spent some time tuning the air/fuel ratio with the AVS, which takes exactly the same tuning parts as the previous AFB. The engine responded favorably to the improved top-end airflow, showing a corresponding bump to the output and pushing the number to a peak of 302 hp at 5,000 rpm.

The Wrap-UpWe went into this test session with kind of a secret goal of achieving a nicely streetable 300 rear-wheel horsepower from our basic 340 Mopar engine package. Using the standard rough estimate method of a 25 percent correction for powertrain losses with an automatic transmission-equipped vehicle on a chassis dyno, this output presumes in the neighborhood of 400 hp at the crank. Given the base of 212 hp and the final number of 302, these bolt-on performance parts yielded a 42 percent increase in power over what we had going in, and that's substantial.

The Weigh-InAs mentioned at the opening of this tale, our '71 Satellite felt surprisingly sprightly given what we knew was a modest engine combination. The 3.91:1 gear ratio in the Mopar 8 3/4 rear certainly had something to do with it, but even so, it just moved pretty well. Acceleration largely comes down to power-to-weight ratio, and at the end of the dyno session, the power was quantified, which left us curious about the weight. APE is equipped with an accurate set of corner scales, so once it was off the dyno, Habrzyk pulled out the scales to assess the mass.

These '71 B-Body Mopars have a reputation for heft, and we were expecting to see the scales top well above 3,600 pounds, even with the small-block and small (904) automatic. It turned out that the weight was not anywhere near what we expected, with the scales showing a total of just 3,354 pounds. We rolled in with a full tank of fuel, of which the better part remained after a total of 32 full-throttle dyno pulls. In comparison with modern muscle cars, this machine is a flyweight, but then it is sans such creature comforts as A/C and a heater (though the underdash equipment for both was still there), and our metal floor lacked any kind of cushy covering.